Once a petroleum well has been drilled and cased, it is often necessary or desired to drill one or more additional wells that branch off, or deviate, from the first well. Such multilateral wells are typically directed toward different parts of the surrounding formation, with the intent of increasing the output of the well. Because the location of the target formation typically falls within a known azimuthal range, it is desirable to control the initial orientation of the deviation fairly precisely.
In order to drill a new borehole that extends outside an existing cased wellbore, the usual practice is to use a work string to run and set an anchored whipstock. The upper end of the whipstock comprises an inclined face. The inclined face guides a window milling bit laterally with respect to the casing axis as the bit is lowered, so that it cuts a window in the casing. The lower end of the whipstock is adapted to engage the anchor in a locking manner that prevents both axial and rotational movement.
It has been found that conventional whipstock supports may be susceptible to small but not insignificant amounts of rotational movement. Hence, it is desired to provide an anchor and whipstock setting apparatus that effectively prevent the whipstock from rotating. It is further desired to provide a system that can set the packer and anchor the whipstock in a single trip. It is further desired to provide an effective whipstock support that can be run in and set using conventional wireline methods.
Furthermore, in prior art devices, disengagement of the whipstock from the orienting key is typically prevented by a shear pin or similar device. The load capacity of this device limits the amount of load that can be placed on the tool. Hence, it is further desired to provide a key element that resists unintentional disengagement while allowing a greater downhole load to be supported by the tool.
In addition, relative rotation of the components of prior art devices is typically resisted by a key or straight spline. The separation of duties (orienting, resisting rotational movement, and resisting axial movement) in the prior art, and the performance of these duties by separate mechanisms resulted in a tool that was relatively complex and susceptible to a variety of failure modes. Hence, it is desirable to provide a tool that combines performance of these duties in, single, robust device.